Prosthetic sphincters for controlling urinary incontinence are well known and in particular the type shown in U.S. Pat. No. 3,863,622 has enjoyed wide-spread use. The contents of that patent are hereby incorporated by reference. The device in that patent, while generally effective, has some shortcomings, particularly in the valve used to control flow from the deflation pump to the reservoir. It has proven difficult to manufacture a valve capable of maintaining pressure in the cuff within a narrow range between that necessary to maintain continence and that at which blood supplies into the urethral tissue would be restricted to the point which would lead to necrosis. The valve must function so as to be able to absorb frequent low level surges in pressure. Such surges can cause the above-referenced system to open the valve enough so that the loss of fluid from the cuff results in the ultimate lowering of system pressure and subsequent incontinence. On the other hand, it is desireable to provide a valve which will release under sudden surges of higher pressure caused for instance by hyperreflexia of the bladder. Such surges, if not relieved may lead to damage to the kidneys due to reflux and hydronephrosis.
It is therefore an object of this invention to provide a predictable and contolled differential between the cracking and holding pressures so as to provide a buffer therebetween. The holding pressure is that pressure necessary to maintain continence while the cracking pressure is that pressure above which systemic damage will result as more fully described hereinafter. The prior art valve, due to its throttling characteristics, does not provide repeatable results.